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18.0 TUNING THE DIGITAL ECU FOR PERFORMANCE
WARNING! The adjustment knobs on the front of the ECU are precision manufactured parts and do not require a great
deal of force to turn. Do not apply excessive force to the adjustment knobs. Full adjustment range for the
knobs is 3/4 of a turn.
WARNING! Initial tuning of the system should be completed in an area free of other boats.
NOTE:
A small change in the adjustment knob settings will have a large effect on the amount of fuel delivered to the engine
under various operating conditions. Make small adjustments to the adjustment knob setting when tuning the system.
NOTE:
Holley recommends the use of a Rich/Lean indicator that will provide information relative to the air and fuel delivery to
the engine when tuning the system. A Rich/Lean indicator with an Oxygen Sensor is available from Holley as P/N 534-
51 and without an Oxygen Sensor as P/N 534-50. Use P/N 534-50 if you have already installed a closed loop kit.
NOTE:
When tuning the system for future closed loop operation, all potentiometer settings must be set slightly richer then
stoichiometric in case an oxygen sensor failure should occur. This will prevent damage to your engine due to lean
operating conditions.
NOTE:
The tuning of the digital ECU is critical in the operation of the fuel injection system and is best accomplished by using a
tachometer. If your vehicle is not equipped with a tachometer, Holley highly recommends one be used. To adjust, follow
the instructions carefully.
18.1 Tuning the Main
As described earlier, the MAIN adjustment knob controls the fuel delivery across the entire operating range by raising or lowering
the fuel delivery 50% above or below the values programmed at the factory. Therefore, adjustments made with the MAIN
adjustment knob will affect the fuel delivery in all modes of engine operation.
1. Disconnect the closed loop harness, if installed, from the rear of the digital ECU. Initial tuning should be completed with the
system operating in open loop mode.
2. Start the engine and allow the engine to reach operating temperature.
3. Turn the adjustment knob labeled MAIN, clockwise until the engine rpm reaches a maximum value and the engine rpm just
begins to drop. If your vehicle is equipped with a Holley rich / lean indicator, adjust the MAIN adjustment knob until the
green center light on the unit remains stable.
4. Rotate the main adjustment knob counter-clockwise back to the point where the engine rpm started to drop, until maximum
engine rpm is once again achieved.
5. Let off the throttle and allow the engine to return to idle. Steps 1 through 5 have given the MAIN a coarse setting, but now
we must continue to tune the MAIN by putting a load on the engine. This will most likely cause the MAIN to go lean.
6. From idle, begin to accelerate the boat until the engine speed is up to 3000 RPM. Note the performance of the engine.
Watch for any signs of black smoke, which indicates a rich condition. If it bogs down the engine may be lean.
7. Bring the boat to a complete stop. Increase or decrease the amount of fuel delivered during the acceleration by turning the
MAIN adjustment knob either clockwise or counter-clockwise. If your vehicle is equipped with a Rich / Lean indicator, adjust
the MAIN adjustment knob until the meter indicates a slightly rich fuel mixture through out the RPM range.
8.
Adjust the MAIN adjustment knob accordingly and continue performing acceleration tests until you achieve a slightly rich
condition through out the entire RPM range of the engine. This will give you a balanced main map.
18.2 Tuning the Idle
Adjustments made to the IDLE adjustment knob will affect the area of the fuel map that relates to the idle operation of the vehicle.
1. Turn the IDLE adjustment knob either clockwise or counter-clockwise until maximum engine rpm is achieved and the engine
idles smoothly. If you are using a rich / lean indicator to tune the system, turn the IDLE adjustment knob until the green
center LED is lit.
